The effect of tobacco products on the periodontium is poorly understood. The use of smokeless tobacco (ST) products has been associated with gingival recession and advanced periodontal disease. Cigarette smoking has also been implicated in the etiology of chronic adult periodontitis although the exact role it plays remains controversial. Several factors probably contribute to the increased levels of oral disease seen in users of nicotine, one of which may be vascular alterations produced by nicotine or oral blood flow. Previous studies have shown that intra-arterial injection of nicotine results in decreased gingival heat diffusion, which is an indirect indicator of blood flow. At present oral blood flow has not been directly measured following either local or systemic delivery of nicotine. The purpose of this study is to examine and compare the clinical and histological effects of locally and systemically delivered nicotine on the periodontal tissues and on blood flow to this region. Nicotine will be topically applied to the oral tissues via an Orabase vehicle in one group of animals. In a second group of animals nicotine will be administered continually via subcutaneous implantation of mini osmotic pumps. Gingival blood flow and periodontal parameters including inflammation and attachment levels will be examined after a 28 day exposure to nicotine in both groups. Blood flow will be measured using the radiolabelled microsphere technique and tissue effects will be evaluated on a clinical and histological basis. The relationship of blood flow to these parameters will be determined. This study will provide information regarding the effects of nicotine on the periodontium and on gingival blood flow, neither of which have been extensively investigated. If blood flow is altered by nicotine administration, this may have important implications in the production of periodontal disease in users to tobacco.